At Williams College in Williamstown, Mass., lint was escaping two clothes-dryer venting systems and spreading throughout a four-story dormitory. Tom Laureyns, president of Four Seasons Heating & Cooling Inc. of nearby Dalton, Mass., identified several causes of the problem.

“Besides the exhaust ductwork not being sealed well, the entire stack was under positive pressure because the existing inline exhaust fan was located in the ceiling, near the dryers,” Laureyns said. “These two factors were causing lint to leak out at every joint in the stack. Furthermore, the existing single-speed fan, which was not designed to handle lint, ran continuously, whether the dryers were being used or not. It was literally sucking tempered air out of the laundry room — a major energy waster.”

Laureyns recommended reconfiguring the system using a dryer venting system made by Tjernlund Products. Not only would it cure the lint problem, it would modulate to match demand, reducing the amount of tempered air being exhausted.

The system Four Seasons installed includes a roof-mounted VSUB modulating fan, a CPC-3 constant-pressure controller, a variable-frequency drive, and a pressure-sensing transducer.

The fan being located at the stack termination on the roof instead of near the dryers creates negative pressure in the stack, which prevents lint from escaping. Exhaust-fan speed is controlled by the CPC-3, which senses static pressure in the common manifold above the dryers. The switch from a continuously running single-speed fan to a fan that ramps up or down to handle the number of operating dryers has resulted in a minimal amount of tempered air being exhausted, as well as major savings on electric heating bills.

Laureyns projects electric-heat savings to add up to more than $25,000 a year. Also, he estimates a 67-percent reduction in operating costs.

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